The present invention relates to a novel light oil (or gas oil) composition and, more particularly, to a light oil composition containing a catalytic cracking-derived light oil having a specific composition and a lubricity improver.
Diesel engines are now widespread in society, mounted on automobiles, ships, construction equipment and the like. The number thereof tends to increase year by year. On the other hand, air pollution by hazardous exhaust gases has become an international problem from the environmental conservation viewpoint and, as regards the exhaust gases from diesel engines, which serve as one of the sources of air pollution, it is now a serious social need to reduce the emission of pollutants.
Endeavors have so far been made in various fields to reduce the contents of nitrogen oxides, particulate matter and like emission matter in the exhaust gases from diesel engines, for example improvements in combustion chamber morphology, provision of exhaust gas recirculating (EGR) systems, of catalyst systems for exhaust gas purification and of particulate matter collecting systems and improvements in the quality of light oils and diesel engine lubricants. The EGR systems, in which the exhaust gas from a diesel engine is circulated again as part of combustion air through the combustion chamber, are regarded as one of promising means. However, they have a number of problems, for example decreases in the durability and reliability of engines, deterioration of lubricants, increases in particulate matter emission and reductions of output as caused by sulfate ions, particulate matter and other substances occurring in exhaust gases. In particular when they are mounted on direct injection type diesel engines which are required to be operated under heavy loads, those problems become serious. Since the sulfate ion is derived from sulfur contained in light oil, such xe2x80x9creduction in the sulfur content in light oilxe2x80x9d as to reduce the sulfur content to 0.05% by weight or below is demanded.
The sulfur content in light oil can be greatly reduced by base oil purification, in particular by catalytic hydrogenation. However, the reduction in sulfur content by such means simultaneously results in decomposition, change in quality or removal of those trace components which occur in the base oil and contribute to lubricant performance, with the result that the lubricant performance of the light oil becomes poor. Light oils with a low sulfur content thus have a problem in that they may cause damages to diesel engine injection pumps. In particular, it is known that when the sulfur content becomes lower than 0.2% by weight, the lubricant performance markedly lowers.
To solve such problems, attempts have so far been made which comprise adding lublicity improvers to low-sulfur light oils. For example, JP Kokai H08-134476 describes a low-sulfur light oil composition which comprises a low-sulfur light oil fraction and at least one additive selected from among diamine dicarboxylic acid salts, diamine monocarboxylic acid salts and monoamine carboxylic acid salts. JP Kohyo H08-505893 describes a fuel oil composition which comprises a low-sulfur liquid hydrocarbon medium quality fuel oil (e.g. diesel fuel) and an additive ester derived from a carboxylic acid containing 2 to 50 cabron atoms and an alcohol containing one or more carbon atoms (e.g. glycerol monooleate).
Further, JP Kokai H11-181452 discloses that a low-sulfur light oil composition which comprises a low-sulfur light oil comprising not less than 0.001% by volume of a straight light oil fraction obtained by atmospheric distillation of a crude oil, with 25 to 200 ppm by volume of a lubricity improver added, has good wear resistance. JP Kokai H11-335678 discloses a lubricant for low-sulfur light oils which comprises a polar fraction separated from a catalytic cracking-derived light oil and containing not less than 25% by volume of bicylcic and polycyclic aromatics as well as a low-sulfur light oil composition containing that lubricant as an additive, and mentions that such a low-sulfur light oil composition can show improved wear resistance without using any expensive lubricity improver.
However, these technologies all comprise incorporating an expensive lubricity improver or a special ingredient in low-sulfur light oils and their lubrication performance-improving effects are not yet satisfactory. Thus, for attaining a desired level of lubrication performance, it is necessary to add a large amount of such a lubricity improver or special ingredient. This produces the problem that the production cost of low-sulfur light oils rises.
An embodiment of the present invention provides a light oil composition having a sulfur content of not more than 0.05% by weight and showing a good lubrication performance at low cost.
The present inventors found that a light oil composition which contains a catalytic cracking-derived light oil containing a specific amount of bicyclic and tri- and polycyclic aromatic compounds can synergistically improve the performance characteristics of lubricity improvers, that, as a result, the level of addition of lubricity improvers can be markedly reduced and that low-sulfur light oils having good lubricant performance characteristics can therefore be produced economically at low cost. Based on such findings, they have now completed the present invention.
Thus, another embodiment of the present invention provides a light oil composition comprising a base oil, not less than 0.01% by volume of a light oil resulting from catalytic cracking and 20 to 200 ppm (on the weight basis) of a lubricity improver, with a total sulfur content of not more than 0.05% by weight, which is characterized in that the light oil resulting from catalytic cracking contains (1) not less than 25% by volume of one or more at least bicyclic polycyclic aromatic compounds and (2) not less than 5% by volume of one or more at least tricyclic polycyclic aromatic compounds.
Preferred embodiments of the present invention include the following:
(1) A light oil composition as mentioned above which contains the above-mentioned catalytic cracking-derived light oil in an amount of 0.05 to 2% by volume.
(2) A light oil composition as mentioned above or mentioned under (1) in which the above-mentioned catalytic cracking-derived light oil contains 30 to 50% by volume of bicyclic and tricyclic aromatic compounds.
(3) A light oil composition as mentioned above or mentioned under (1) or (2) in which the above-mentioned catalytic cracking-derived light oil contains 10 to 20% by volume of tricylic polycyclic aromatic compounds.
(4) A light oil composition as mentioned above or mentioned under any of (1) to (3) in which the above-mentioned lubricity improver is an ester compound.
(5) A light oil composition as mentioned above or mentioned under any of (1) to (4) in which the content of the above-mentioned lubricity improver is 40 to 160 ppm by weight.
(6) A light oil composition as mentioned above or mentioned under any of (1) to (4) in which the content of the above-mentioned lubricity improver is 60 to 120 ppm by weight.
The present invention may comprise, consist, consist essentially of the steps or elements recited herein and may be practiced in the absence of a step or element not recited, and includes the methods using the compositions to enhance lubricity in diesel engines.